post_encoding.rb

# A monkey-patch for ActionPack, which takes into account a POST's encoding.
# Browsers may specify this using a hidden _charset_ field, or in the Content-Type.
# Briefly tested on Rails 2.3.5 and Ruby 1.9.1p376.

class ActionController::Request < Rack::Request
  # This is copied from Rack::Request. Rails overrides content_type, which the original relies on,
  # thus breaking it, unfortunately. Instead, this version uses @env['CONTENT_TYPE'].
  def media_type_params
    return {} if @env['CONTENT_TYPE'].nil?
    @env['CONTENT_TYPE'].split(/\s*[;,]\s*/)[1..-1].
      collect { |s| s.split('=', 2) }.
      inject({}) { |hash,(k,v)| hash[k.downcase] = v ; hash }
  end

  # Our override for handling charset. (Indirectly affects #params)
  def POST_with_url_encoded_form_charset
    handle_url_encoded_form_charset(self.POST_without_url_encoded_form_charset)
  end
  alias_method_chain :POST, :url_encoded_form_charset
  alias_method :request_parameters, :POST

  private
    def handle_url_encoded_form_charset(form)
      # FIXME: have a default charset setting?
      # FIXME: check for x-www-form-urlencoded? Only that format allows the _charset_ field
      encoding = content_charset || form['_charset_']
      if encoding
        recursively_force_encoding(form, encoding)
      else
        form
      end
    rescue ArgumentError
      # The client specified an encoding we do not understand.
      form
    end

    # A recursive variant of String#force_encoding, which works with Hashes and Arrays too.
    def recursively_force_encoding(value, encoding)
      case value
      when Hash
        h = {}
        value.each { |k, v| h[k] = recursively_force_encoding(v, encoding) }
        h
      when Array
        value.map { |e| recursively_force_encoding(e, encoding) }
      when String
        value.force_encoding(encoding)
      else
        value
      end
    end
end

module ActionView::Helpers::FormTagHelper
  # Our override for adding the hidden _charset_ field.
  def extra_tags_for_form_with_charset(html_options)
    extra_tags_for_form_without_charset(html_options) +
        tag(:input, :type => 'hidden', :name => '_charset_')
  end
  alias_method_chain :extra_tags_for_form, :charset
end